Changes in populations and species (25 hours)
The types of living organisms that have inhabited earth have changed over time. Fossil and other evidence indicates that there has been a progressive development of organisms
from simple to more complex in structure that have been able, through structural, physiological and behavioural adaptations, to exploit different parts of the environment and
utilise different resources within a particular habitat. Competition for resources and physical changes in environments favours changes in the frequency of particular traits in a
population. Different traits arise as a result of chance mutations within the reproductive cells of individuals in a population. New species arise when traits in different populations
become so different that members of the different populations develop intrinsic isolating mechanisms that prevent interbreeding.
Key Concepts:
3. Organisms live an interdependent existence in environments to which they are adapted.
4. Changes in the living world occur in different scales of time and space.
5. There are processes in place which maintain dynamic equilibrium at all organisational levels.
6. There are mechanisms by which characteristics of individuals in one generation are passed on to the next generation.
UNIT ORGANISATION
Main Focus
Key
Ideas
Biological evolution
19, 21
Examine theories and evidence that have led to the
development of modern theories of biological
evolution through natural selection.
Variations in populations
19, 22,
24
Gain an understanding that within any population
there are variations in a large number of inherited
traits, the mean of each representing the best
adaptation for that environment. Differential mortality
of the extreme variations occurs. Changes in
environmental conditions can result in changes in
differential mortality and thus the mean for the trait.
The gene pool
22, 24
Understand how changes in populations result from
changes in types and frequency of alleles as a result of
mutations and environmental selection pressures.
Suggested Expansion of the Main Focus
Possible Student Activities and
Learning Experiences
Examine fossils.
Draw a time scale of fossil
occurrences.
Analyse biochemical similarities
and differences between
organisms to propose a possible
evolutionary relationship.
Investigate the variation of a trait
within an age and gender group
within the school. Apply
statistical test to determine
significance difference in the
trait. Propose a possible
environmental advantage for the
mean.
Apply the Hardy–Weinberg Law
to a human trait. Report on the
likelihood that genetic
equilibrium can exist in any
situation.
Skills
Objectives
Text Reference
5
UB, IB
Ch. 22
6
UB, IB
Ch. 23.1
6
UB, IB
Ch. 23.2
Changes in populations and species
UNIT ORGANISATION
Main Focus
Speciation
The human species
Continued
Key
Ideas
Suggested Expansion of the Main Focus
25
Examine the types of variations that exist between
adjoining populations, the formation of races and
models of geographic isolation that can lead to
intrinsic isolating mechanisms and new species.
Changes in one species through natural selection can
act as a selection pressure on other species (coevolution). Homeostatic mechanisms within a species
have a tendency to maintain species integrity and it
may require a sudden dramatic environmental
pressure to bring about divergent speciation.
25
Realise that the human species has undergone
evolutionary changes that show relationship with
other primates.
Possible Student Activities
and Learning Experiences
Video analysis of ‘The
Vampire Finches of the
Galapagos’.
Compare and contrast
structural, biochemical,
physiological and behavioural
features of humans and
primates.
Use the fossil record to
establish a time line and steps
in the evolution of modern
humans.
Skills
Objectives
Text
Reference
UB
Ch. 23.3
Ch. 23.4
Ch. 23.5
UB, IB
Ch. 23.6